Early head injury and attention deficit hyperactivity disorder: retrospective cohort study

OBJECTIVE To explore the hypothesis that medically attended head injury in young children may be causal in the later development of attention deficit hyperactivity disorder. DESIGN Retrospective cohort study. SETTING Health improvement network database (1988-2003), a longitudinal UK general practice dataset. PARTICIPANTS All children registered in the database from birth until their 10th birthday. MAIN OUTCOME MEASURES Risk of a child with a head injury before age 2 developing attention deficit hyperactivity disorder before age 10 compared with children with a burn injury before age 2 and children with neither a burn nor a head injury. RESULTS Of the 62 088 children who comprised the cohort, 2782 (4.5%) had a head injury and 1116 (1.8%) had a burn injury. The risk of diagnosis of attention deficit hyperactivity disorder before 10 years of age after adjustment for sex, prematurity, socioeconomic status, and practice identification number was similar in the head injury (relative risk 1.9, 95% confidence interval 1.5 to 2.5) and burn injury groups (1.7, 1.2 to 2.5) compared with all other children. DISCUSSION Medically attended head injury before 2 years of age does not seem to be causal in the development of attention deficit hyperactivity disorder. Medically attended injury before 2 years of age may be a marker for subsequent diagnosis of attention deficit hyperactivity disorder.